The over-all aim of the proposed research project is to determine whether, with progressive aging, the loss in bone formation ability is due to bone cell alterations intrinsically linked to the age of the tissue, or is the result of a suboptimal environment found in the aging host. Tissue culture and grafting techniques will be employed to study bone formation as a function of age. Environmental factors will be modified in vitro and in vivo in an attempt to extend the age at which new bone formation is lost or significantly depressed in bone tissue or isolated bone cells.